Atomic collisions with relativistic heavy ions. VIII. Charge-state studies of relativistic uranium ions

Abstract

Charge-state distributions were measured for incident 105-, 220-, 430-, and 955-MeV/amu U ions on thin and thick solid targets. Initial bare, one-, two-, three-, nine-, and 24-electron ions were used, so that single and multiple ionization of K-, L-, and M-shell electrons and electron capture into bare ions and into ions having initially full or partially full K and L shells could be observed. Multiple-ionization effects in two-electron U ions and in ions having many electrons in the K, L, and M shells are calculated by using the semiclassical approximation and assuming binomial statistics. Binding effects on K-shell ionization are compared with previous measurements using relativistic Xe ions, and with the Glauber theory. For 430- and 955-MeV/amu U ions, good agreement is obtained between measured capture cross sections and calculated radiative and nonradiative (eikonal-approximation) cross sections. Some disagreement is found at lower energies. An approximate model is proposed for multiple-capture cross sections. Finally, the measured equilibrium charge states are compared to ground-state models and to models including excited-state effects. Excited-state effects are less important for relativistic U ions than for any other ion in matter. Differences between the excited- and ground-state models are found to be too small to be observed.